Gaheris and other Round Table knights visit King Mark's court and report Tristram's great deeds. While they are there a challenge comes to Mark's court from Ywain of the Round Table. None of Mark's knights can withstand him, and the visiting Round Table knights are sworn never knowingly to ride against a fellow Round Table knight except in sport. In idiotic fury, Mark himself attacks Ywain — from ambush. Kay scoffs at Mark's cowardice and rebukes him for sending his best knight, Sir Tristram, into exile. Spitefully, Mark and Andret decide to waylay Kay and Gaheris. They put on black clothes so that they won't be seen in the dark, forgetting that it is a bright moonlit night. Kay and Gaheris easily trounce them.
Meanwhile the jailor of Tristram, Palomydes, and Dynadin reconsiders and releases the knights from prison. Dynadin encounters the murderer of knights, Bereuse Saunz Pit (whose later death at Gareth's hands has already been recounted), and puts him to flight. Tristram falls into Morgan's hands and is tricked into bearing for her a shield designed to embarrass Launcelot and Guinevere. He uses the shield in a tournament where he unhorses both Arthur and Ywain.
Afterward, riding in a forest, Tristram finds Bereuse Saunz Pit about to murder Palomydes. He rescues his old enemy, drives off Bereuse, and sets a time and place for battle with Palomydes. They will fight beside the old tomb of Lanceor (see "The Knight with the Two Swords"). As they ride on they find a strange knight with a covered shield sleeping under a tree. They wake him; he mounts his horse and jousts them both to the ground, then gallops off. Tristram finds later that the stranger has slain another Round Table knight, has wounded Gawain and Bleoberys, and has shamed Kay and Dynadin.
Tristram rides to the appointed place for his fight with Palomydes — the tomb of Lanceor, where long ago Merlin prophesied that the two greatest knights and the two greatest friends in the world would fight. There he finds the knight with the covered shield and fights him. At last, both badly wounded, Tristram and Launcelot discover one another's identity and the fight stops. They go to Camelot, where Launcelot explains that, riding incognito, he was forced into battle with Round Table knights. Tristram is made a knight of the Round Table and all the court rejoices.